Collision warning systems, primarily for use in road vehicles, are being developed and tested. In a typical system of this nature, a sensor (referred to as a Forward Looking Sensor or FLS) is mounted at the forward end of a host vehicle and provides data representative of the range of a target vehicle or other object, the range rate, and the azimuth angle of the target. The range is the distance between the host and the target, the range rate is the rate of change of the range, and the azimuth angle is the angle in a horizontal plane between the target and the direction of travel (the path or trajectory) of the host vehicle. A microprocessor receives the data plus path prediction data (from the yaw rate and the speed of the host vehicle), and calculates whether a collision is likely. An alarm may be sounded, the throttle may be backed off, and/or the brakes may be applied by the system, to avoid a collision.
A system generally as described above may also be incorporated in an Intelligent Cruise Control (ICC) system and operate to adjust the vehicle speed to maintain an appropriate timed headway or following distance.
As mentioned above, a system of this character provides a close estimate of the location of the target relative to the path of travel of the host vehicle. A close estimate, in turn, has in the past required that the FLS viewing axis be closely aligned, in a horizontal plane, with the axis of the host vehicle (the direction of travel) so that the range and azimuth angle relative to the host vehicle may be accurately estimated.
Such FLS sensors rely on radar, laser or ultrasonic signal transmitter/receivers, and typical installation tolerances in vehicle assembly at the factory do not normally meet the required accuracy of alignment. A more precise mechanical alignment at the factory or at a service facility is possible but it would be time consuming and costly.
Even if a practical arrangement were feasible for accurately aligning the FLS with the vehicle axis during manufacture, it would not solve all problems. For example, there might be subsequent changes in the FLS alignment during usage and/or misalignment relative to the path of travel of the host vehicle caused by vehicle "crabbing" (wherein the vehicle axles are not perpendicular to the path of travel) which would not be detected.
It is a general object of the present invention to avoid the foregoing problems by providing improved apparatus and method for automatically sensing, during operation of a host vehicle, any misalignment of the sensor, and for automatically compensating for any misalignment.